During fabrication of semiconductor devices a wafer of base material, such as crystalline silicon, is used to form electrical components. The process steps to form the semiconductor device are generally additive or subtractive steps. These can include, but are not limited to, growing materials, depositing materials, implanting ions, planarizing a surface, and etching material. These processes are performed on the wafer which is then singulated into separate semiconductor die. Each die includes an active surface, or top surface, where the process steps are performed to form the electrical devices, and a back surface.
After singulation, the semiconductor die can be packaged for use in other devices, such as consumer electronic products. Several methods have been used to form electrical connections with the semiconductor active surface, such as wire bonding and ball bonding. As an example, one process for packaging a semiconductor die includes (a) forming dice on a semiconductor wafer, (b) cutting the wafer to separate or singulate the dice, (c) attaching individual die to an interposer substrate, (d) wire-bonding conductive bond-pads of the active surface of the die to terminals of the interposer substrate, and (e) encapsulating the die with a suitable moulding compound.
In response to the desire to increase the density of semiconductor devices for a given footprint, semiconductor manufacturers have worked to develop ways to stack one or more devices on top of another. Different methods for electrically connecting the semiconductor die together have been described. These methods can include forming back side conductive interconnect locations. Some examples of backside interconnects are described in U.S. Pat. Nos. 6,582,992, 6,903,443, 6,962,867 and 7,091,124.
For example, the U.S. Pat. No. 7,091,124 patent describes forming vias or passages through a die and a bond-pad on an active surface of the die to a back side of the die. The U.S. Pat. No. 6,962,867 patent describes a semiconductor substrate including one or more vias having conductive material formed therein and which extend from an active surface to a back surface of the semiconductor substrate. A method for fabricating semiconductor components and interconnects, described in the U.S. Pat. No. 6,903,443 patent, includes the steps of providing a substrate, such as a semiconductor die, forming external contacts on opposing sides of the substrate by laser drilling vias through the substrate, and forming conductive members in the vias. The U.S. Pat. No. 6,582,992 patent describes conductive grooves formed on the edges of a die that function as interlevel conductors for a stacked die package.
Forming vias after the semiconductor processing is substantially complete can be referred to as a via-last process. In contrast, some development work has been done to form the via prior to integration processing, a via-first process. For example, a polysilicon via process was disclosed in “A 3D Stacked Memory Integrated on a Logic Device Using SMAFTI Technology,” Kurita, et al., 2007 Electronic Components and Technology Conference, pages 821-829. The paper describes a via-first process with a highly doped poly-Si as the filling material for through silicon vias in DRAM dice. The Si substrate etching and filling are carried out before the DRAM device process in the via-first process. The paper indicates that the choice of poly-Si as the filling material can prevent metal atom contamination and temperature restriction in the device process that follow. As described in the paper, a trench is etched into a silicon substrate and the trench side-wall is isolated with thermal oxide. Poly-Si is deposited by Chemical Vapor Deposition (CVD) and the silicon surface is planarized with Chemical Mechanical Polishing (CMP) to remove excess layers at the top surface. A DRAM device process is then carried out on the wafer.
For reasons which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative methods and devices that provide back side conductive interconnect locations for semiconductor devices.